MOSFET (Metal Oxide Silicon Field Effect Transistor) devices may fall within one or more classes of devices, such as high-voltage and low-voltage devices. Low voltage MOSFETs may be configured to operate at a voltage generally less than 5 volts, such as by operating at equal to or less than approximately 3-4 volts, and high voltage MOSFETs may be configured to operate at less than generally 40 volts. Devices such as these may have varying structural differences, such as differing channel regions with differing dopant concentrations, to provide particular capabilities for operating at particular voltages, and may additionally have varying formation processes. The semiconductor industry uses a variety of methods for creating high-voltage devices (i.e., JFETS, DMOS, BiCMOS, and others).
Products such as displays, ink jet printers, sensors, and others often require the incorporation of high-voltage controls in the circuit designs that support the product. A capability to integrate high-voltage devices and low-voltage devices into the same circuit design can reduce the cost of the product and can result in a higher performance product.
For example, it may be desirable to perform a process for making a CMOS (complementary metal oxide semiconductor) integrated circuit formed on a substrate to allow having one or more MOSFETs that may be capable of operating at high voltages and one or more MOSFETs that may be capable of operating at low voltages. However, the formation of active devices such as these may involve modifying a low voltage formation process with additional masking, implanting, and thermal cycle processes. These additional process steps may disrupt the conventional process flow and may involve the expenditure of additional time or expense. It is desirable to enable integration of high-voltage CMOS capability with low-voltage CMOS circuitry without extensively modifying the low voltage performance.
FIG. 1C is a magnified view of detail 28 of FIG. 1B. FIG. 2C is a magnified view of detail 29 of FIG. 2B. FIG. 3C is a magnified view of detail 30 of FIG. 3B. FIG. 4C is a magnified view of detail 31 of FIG. 4B.